The present invention relates generally to methods and apparatus for cooling patients for therapeutic purposes, and more particularly to systems for treating brain trauma and brain ischemia by inducing hypothermia in a patient.
It has been discovered that the medical outcome for a patient suffering from severe brain trauma or from ischemia caused by stroke or heart attack is degraded if the patient""s body temperature rises above normal (38xc2x0 C.). It is further believed that the medical outcome for many such patients might be significantly improved if the patients were to be cooled relatively quickly to around 32xc2x0 C. for a short period, e.g., 24-72 hours.
The affected organ, in any case, is the brain. Accordingly, systems and methods have been disclosed that propose cooling blood flowing to the brain through the carotid artery. An example of such systems and methods is disclosed in co-pending U.S. patent application Ser. No. 09/063,984, filed Apr. 21, 1998, owned by the present assignee and incorporated herein by reference. In the referenced application, various catheters are disclosed which can be advanced into a patient""s carotid artery and through which coolant can be pumped in a closed circuit, to remove heat from the blood in the carotid artery and thereby cool the brain. The referenced devices have the advantage over other methods of cooling (e.g., wrapping patients in cold blankets) of being controllable, relatively easy to use, and of being capable of rapidly cooling and maintaining blood temperature at a desired set point.
As recognized in co-pending U.S. patent application Ser. No. 09/133,813, filed Aug. 13, 1998, owned by the present assignee and incorporated herein by reference, the above-mentioned advantages in treating brain trauma/ischemic patients by cooling can also be realized by cooling the patient""s entire body, i.e., by inducing systemic hypothermia. The advantage of systemic hypothermia is that, as recognized by the present assignee, to induce systemic hypothermia a cooling catheter or other cooling device need not be advanced into the blood supply of the brain, but rather can be easily and quickly placed into the relatively large vena cava of the central venous system. Moreover, since many patients already are intubated with central venous catheters for other clinically approved purposes anyway, providing a central venous catheter that can also cool the blood requires no additional surgical procedures for those patients. A cooling central venous catheter is disclosed in the present assignee""s co-pending U.S. patent application Ser. No. 09/253,109 filed Feb. 19, 1999 and incorporated herein by reference.
The present invention recognizes that a patient requiring hypothermia preferably be cooled down rapidly, at a rate of two degrees or more an hour. Thus, catheters with high cooling capacities, such as the catheter that is the subject of the second of the above-referenced applications, are desirable. As recognized herein, however, it is not necessary to maintain a high capacity catheter in a patient once the patient has been cooled, provided a catheter with lower cooling capacity is used to maintain temperature at the desired level. The present invention understands that such a lower cooling capacity catheter, which can be configured as, e.g., a central venous catheter to facilitate uses other than just cooling, can be advantageously used to replace the higher capacity catheter to maintain temperature.
A kit for lowering and maintaining a feverish patient""s temperature to normal body temperature or below includes a first catheter that has at least one fluid circulation passageway connectable to a source of coolant. In accordance with the present invention, the first catheter is configured for placement in a patient""s circulatory system, and the first catheter is characterized by a first cooling capacity. Also, a second catheter has at least one fluid circulation passageway connectable to a source of coolant. As set forth below, the second catheter is configured for placement in a patient""s circulatory system, with the second catheter having a second cooling capacity that is less than the first cooling capacity.
In a preferred embodiment, the kit can include the source of coolant. Preferably, the source of coolant includes at least one thermal electric cooler (TEC) for heating or cooling coolant such that coolant is returned to the catheter to heat or cool the catheter.
In a particularly preferred embodiment, the first catheter includes a heat exchange region that in turn includes at least one hollow fiber. Moreover, the second catheter is configured as a central venous catheter, and it includes a heat exchange region that includes at least one balloon.
In another aspect, a method for establishing and maintaining normal body temperature or hypothermia in a patient includes establishing the desired temperature in the patient using a high cooling capacity catheter placed in the venous system of the patient. The desired temperature is then maintained in the patient using a central venous catheter having a heat exchange region.